Which shopping cart have you used? I have listen that Magento is the best SEO friendly shopping cart among all.

yep… I do agree with you. SEO friendly coding helps your custom Magento website to gain high rankings in SEs. It also gives you Auto generated Google Sitemap, Meta for your products and category pages and much more…

If you Already search Keyword & want to that keyword traffic then search related page in your site & Do that URL for SEO. If that URL has a 2 and 3 Pages then do the snippet code with Next & Pre meta tag. Snippet code is more important tools now in ecommerce site. You can Search more in google Webmaster tool .

If you done your keyword research than you doing On page and Off page optimization for your site.
In Off page optimization, you target your main product first than you may target other keyword for getting user and also high sales for their site.